Photoemission spectrum

Values for the lattice constant a, Neel temperature T, paramagnetic Curie temperature 0p, Curie constant C, and absolute thermoelectric power a at room temperature for a CeSeo.sSo.s single crystal are compared with data for CeS and CeSe single crystals all samples obtained from melt  

The mixed crystal like the endmembers exhibits p-type conduction. The crystal electric field splitting A/k was 120 K for CeSeo.sSo.s in comparison to A/k 130 K for CeS and A/k 100 K for CeSe, F. Hulliger, B. Natterer, H. R. Ott (J. Magn. Magn. Mater. 8 [1978] 87/98, 92). 

A mixture of the elements was either melted in an induction furnace and cast or pressed and then annealed for a few hours at 1500°C, Smirnov et al. [1]. 

An X-ray phase analysis showed Ce3Se4 to have a well developed Th3P4 lattice. However, the samples studied contained a great amount of a second phase [1]. The lattice constant is a = 8.973 A, Starovoitov et al. [2]. 

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Many phenomena in solid-state physics can be understood by resort to energy band calculations. Conductivity trends, photoemission spectra, and optical properties can all be understood by examining the quantum states or energy bands of solids. In addition, electronic structure methods can be used to extract a wide variety of properties such as structural energies, mechanical properties and thennodynamic properties. 

The accuracy of most TB schemes is rather low, although some implementations may reach the accuracy of more advanced self-consistent LCAO methods (for examples of the latter see [18,19 and 20]). However, the advantages of TB are that it is fast, provides at least approximate electronic properties and can be used for quite large systems (e.g., thousands of atoms), unlike some of the more accurate condensed matter methods. TB results can also be used as input to detennine other properties (e.g., photoemission spectra) for which high accuracy is not essential. 

Fig. 11. Composition dependence of the resistivity p x) for thick films of Cbo doped with Na, K, Rb, and Cs. Points indicate where exposure to the alkali-metal source was stopped and x-ray and ultraviolet photoemission spectra were acquired to determine the concentration x. The labels indicate the known fulleride phases at 300 K. The minima in p x) occur for stoichiometries corresponding to NaQCeo, K.iCeo and Cs,.,.Cfio[ll3].

We clearly demonstrated that, in going from a bulk CusPt to an overlayer on platinum, the influence of the substrate reflects in the photoemission spectra and that its consideration improves the agreement with the experimental data. 

Figure 2.41. X-ray photoemission spectra of Fe foil after CO hydrogenation at 548 K in CO/H2=1 20 at 1 bar total pressure and varying reaction times, (a) C Is spectra from K-free Fe. (b) K 2p and C Is spectra from K-covered Fe, Ok -OA 28 Reprinted with permission of the American Chemical Society.

The photoemission spectra of the GFP in buffer solution and of the hybrid material GFP/SBA-15, are reported in Figure 4. All samples were excited at 475 nm and show a well resolved photoemission band at 502 nm with a shoulder at 536 nm. The shape of the emission profile for GFP/SBA-15 follows closely that of the GFP in buffer solution, but the intensity of the signal is higher in the case of the hybrid. This result evidences that the photoemission efficiency is enhanced by the protein confinement inside the mesoporous channels. 

Figure 4. Photoemission spectra of GFP in buffer solution (dotted line) and GFP/SBA-15 (solid line).

Backer, M. W. Pernisz, U. C. Photoexcitation and Photoemission Spectra of Phenyl-Substituted Cyclosiloxanes. In Synthesis and Properties of Silicones and Silicone-Modified Materials Clarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Van Dyke, M. E., Eds. ACS Symposium Series 838 American Chemical Society Washington, DC, 2003 pp 105-116. 

The discussion on the experimental evidence for the existence of roughening on low indexed surfaces is not yet settled. Let us consider for example the Cu(110) surface. More than ten years ago it had been noticed that the intensities in the photoemission spectra taken from Cu(l 10) decrease rapidly with temperature above 500 K Similar effects have been seen recently in... 

Figure 14.1 QD-MBP-dye nanoassembly, (a) Schematic representation of the QD-MBP-dye nanoassembly used (not drawn to scale). The distance r represents the average distance between the QD center and the Cy3-labeled residue on MBP. (b) Normalized absorption spectra of Cy3 dye and photoemission spectra of three CdSe-ZnS core-shell QD solutions demonstrating the ability of tuning the spectral overlap of the QD with a given dye acceptor. Adapted from reference 28 and reprinted by permission of the American Chemical Society.

Since electrons are much faster than nuclei, owing to Wg Mj, ions can be considered as fixed and one can thus neglect the //ion-ion contribution (formally Mion-ion Hee, where Vion-ion is a Constant). This hrst approximation, as formulated by N. E. Born and J. R. Oppenheimer, reflects the instantaneous adaptation of electrons to atomic vibrations thus discarding any electron-phonon effects. Electron-phonon interactions can be a-posteriori included as a perturbation of the zero-order Hamiltonian Hq. This is particularly evident in the photoemission spectra of molecules in the gas phase, as already discussed in Section 1.1 for nJ, where the 7T state exhibits several lines separated by a constant quantized energy. 

Figure 6.25. Valence band photoemission spectra of 1 ML Ceo on a Ag(lOO) surface as a function of potassium doping. Also shown are the spectra of the clean Ag(lOO) surface and of a Ceo multilayer (bottom). All binding energies are referred to the L f of polycrystalline silver. Reprinted from Surface Science, Vols. 454-456, C. Cepek, M. Sancrotti, T. Greber and J. Osterwalder, Electronic structure of K doped Ceo monolayers on Ag(OOl), 467 71, Copyright (2000), with permission from Elsevier.

Franck-Condon energy, 21 188, 189 photoemission spectra, 21 186 leghemoglobin reaction, 46 524... 

A satellite is found in the valence band spectrum of Ni metal (and compounds) at about 6 eV from Ep . This satellite does not correspond to any feature in the calculated density of states. Therefore a brief discussion of this satellite is worthwhile, since its interpretation has inspired that of some structures found in light actinide metals photoemission spectra. 

No photoemission spectra are unfortunately available for Np metal, in the tight actinide 5 f itinerant side, and on Cm, Bk, Cf, etc. on the heavy actinide 5 f localized side. It is worthwhile to stress the need for good photoelectron evidence on these systems in order to shed more light on the elemental actinide metals series. 

Partial localization of the 5 f states in the light actinides (line III of subsection b) might cause the appearance of satellite structures at energies not very far from Ep in their valence band photoemission spectra. If such structures could be convincingly demonstrated, important information would be added to the theoretical analysis of the locahza-tion vs. itineracy problem of the actinide metal series. 

Figure 17 is a clear illustration of the Mott-Hubbard transition in the actinide series the 5f emission occurs, for a-Pu, at Ep, indicating a high 5f-density of states pinned at the Fermi-level, whereas the 5 f emission occurs at lower energy for americium metal. In this case, therefore, a theoretical concept deduced indirectly from the physical properties of the two metals, finds direct (one might even say photographic ) confirmation in the photoemission spectra. 

Eberhardt et al. (22a) have studied the photoemission of oxygen physi-sorbed on graphite at 10 K. The photoemission spectra exhibit vibrational structure in the 2n band. From calculations based on Franck-Condon factors, the authors conclude that on the graphite surface the equilibrium distance of the oxygen nuclei is decreased by 0.065 A relative to the gas phase. This would also be consistent with a partial electron withdrawal from oxygen antibonding orbitals into available orbitals in the graphite. 

Gopel et al. (135a) have reported ultraviolet photoemission spectra (UPS) of the interaction of 02 with the (lOlO) face of a single crystal of ZnO. Between 300 and 600 K, chemisorption of oxygen is observed on stoichiometric ZnO (lOlO) surfaces and UPS difference spectra indicate peaks at... 

Figure 7.7(a) shows the Is photoemission spectra of MgO(lOO) following reaction with different concentrations of water vapor. Liu et al. [143] interpreted these spectra as indicating that water vapor reacts primarily with defect sites on the Mg(100) surface at p(H20) < 10 4 torr and with terrace sites at p(H20) > 10-4 torr. 

The important role played by defect density in chemical reactivity can be seen in Figure 7.8, which shows Is photoemission spectra of a vacuum-cleaved, clean MgO (100) surface in comparison with (1) the Is spectrum of a vacuum-cleaved MgO (100) surface exposed to 2.3 x 10-8 torr p(H20) for 3 min, (2) the spectrum of an MgO (100) surface purposely cleaved off angle in vacuum then exposed to p(H20) = 3 x 10-8 torr for 3 minutes, and (3) the spectrum of an MgO (100) surface that was Ar+ ion sputtered and then exposed to p(H20) = 2.5 x 10 x torr... 

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